The objective of the present invention is to provide an efficient, reliable and economical method for separating the pith from the bast of sweet sorghum or sugar cane, as where the sugar-laden pith of sweet sorghum is being used in the making of fuel alcohol. The process is also applicable to other bast-producing plants yielding jute and cordage fibre.
An equally important object of the invention is to provide a rugged and durable apparatus of great simplicity for practicing the process on the basis of an hourly throughput.
U.S. Pat. No. 3,567,510, Tilby, issued Mar. 2, 1971, discloses a method and apparatus for separating components of sugar cane. More particularly, the Tilby patent deals with separating the pith, rind and epidermis of split sugar cane stalks. The split stalk is flattened and milled on the pith side to separate the pith from the rind, and is milled on the opposite side to remove the epidermis. While the objectives of the Tilby patent are admirable, the apparatus has proven in practice to be so mechanically complex that it has yet to become a machine fit for everyday commercial usage. Only a very small commercially inadequate throughput can be realized with the Tilby method and apparatus.
In contrast to the known prior art, the present invention provides a method and apparatus of extreme simplicity resulting in a commercially feasible product output. Features of the apparatus which distinguish it from the prior art are:
(1) A flail blade speed substantially slower than the blade speeds of chippers, choppers or cutters.
(2) A dull flail element which does not cut through the rind fibres except at the nodes where the fibres lack continuity. The dull blade requires little if any maintenance which is a marked advantage over machines employing sharp blades.
(3) All of the depithing of a given incremental stalk section is accomplished by a single pass of the flail element in coaction with a spaced stationary reaction bar, so that no subsequent reprocessing is required.
(4) The invention mechanically produces pith particles on the one hand and rind fibres on the other hand. Separation of these two components is readily accomplished by a coarse vibrating screen or elutriation techniques.
(5) The apparatus is characterized by very few moving parts, all of a rotational nature, ruggedness hence reliability, and low cost of parts and assemblies.
The apparatus used to practice the method in accordance with the invention should not be confused with certain prior art devices bearing some superficial similarities to this invention. For example, shear-bar forage choppers cut whole stalk corn or the like in the field. This material is compressed into a mat and fed into a cylindrical cutter by means of which it is chopped into pieces of desired size, generally 1.3 cm. for corn. Knife speeds for such choppers of 30-33 m/sec. are common on direct throw models and 18-24 m/sec. with an auxiliary impeller blower to blow the chopped material into a trailing forage wagon.
Similarly, disc chippers are commonly seen and well known in disposing of woody trash and operate in the same general manner, sharp blades chipping a wooden stalk or limb into small particles. Neither of the above is similar to the present invention in actuality, as will appear during the course of the following description.